docs: def get_platform_variables(ds):
      '''
      Returns a list of platform variable NAMES
  
      :param netCDF4.Dataset ds: An open netCDF4 Dataset
      '''
      candidates = []
      for variable in ds.variables:
          platform = getattr(ds.variables[variable], 'platform', '')
          if platform and platform in ds.variables:
              if platform not in candidates:
                  candidates.append(platform)
  
      platform = getattr(ds, 'platform', '')
      if platform and platform in ds.variables:
          if platform not in candidates:
              candidates.append(platform)
      return candidates